1. Field of the Invention
The invention herein refers to a vehicle air bag, and more particularly to a driver's side vehicle air bag adapted to deploy in a controlled manner.
2. Prior Art
Many modern vehicles incorporate one or more inflatable air bags for the protection of occupants in the event of a crash. The air bags are mounted in a folded, compact condition in conjunction with a gas generator, and upon sensing of a vehicle crash, the gas generator produces inflation gas which rapidly deploys and inflates the air bag.
The driver's side air bag is typically mounted in the hub of a steering wheel and deploys toward the driver as the driver experiences relative motion toward the wheel and deploying air bag. The thrust or main axis of deployment of the air bag is directly toward the driver, and the material of the air bag initially forms an elongated column, the end of which may strike the driver (sometimes in the face) occasionally resulting in abrasions. As the gas generator continues to provide inflation gasses, and the air bag then fills laterally to provide the desired broad cushion. The formation and travel of the initial elongated column of air bag material is in large part a result of inertia provided to the material of the air bag upon initial rapid deployment, and is not solely a function of inflation pressure within the air bag.
Driver's side air bags have been provided with internal tether straps to restrain the range of initial inertial deployment toward the driver. Two to four anchored tether straps have their ends secured to the front panel of the air bag to limit the extent of deployment of the front panel toward the driver. This tether strap system, although efficient in limiting the extent of deployment, has some drawbacks of its own. The tether straps add concentrated points of mass to the front panel and this additional mass in part exacerbates the problem in that more kinetic energy is developed and imparted to the driver if the air bag reaches the driver, with a consequent greater chance of injury. The tether straps also cause stress concentration at the attachment points, thereby requiring additional reinforcement to prevent failure of the air bag. Further, the tether straps add bulk and weight to the air bag module, when it is desirable to keep the module as light and compact as possible for mounting in the steering wheel hub.
Accordingly, there is a need for better control in the deployment of a driver's side air bag while retaining simplicity and reliability in the manufacturing and operation thereof.